(a) Technical Field
The present disclosure relates in general to an exhaust heat recovery device. More particularly, it relates to an exhaust heat recovery device, which recovers and reuses waste heat of exhaust gas that is discharged from an engine of a vehicle.
(b) Background Art
Recently, research has been aimed at improving fuel efficiency by recovering and reusing energy discharged from a vehicle.
Examples of technologies of recovering or reusing waste energy include:
(1) Thermoelectric conversion technology and thermoacoustic conversion technology using waste heat;
(2) Piezoelectric technology and electromagnetic induction technology using vibration and sound generated by the vehicle; and
(3) Wind energy regeneration technology using aerodynamic movement, regenerative shock absorber technology using aerodynamic perturbation, and nanogenerator technology using vortex energy.
A typical example of the energy recovery and reuse technology applied to the vehicle is an exhaust heat recovery device.
Japanese Patent Publication No. 2007-247556, incorporated by reference in its entirety herein, discloses an exhaust heat recovery device, which recovers waste heat of exhaust gas by heat exchange between the exhaust gas, which flows through a bypass channel in a housing, and a coolant medium, which flows through a coolant medium channel provided adjacent to the exhaust channel.
For example, FIG. 1 shows an exhaust heat recovery device, which recovers exhaust heat by heat exchange between exhaust gas and coolant.
These exhaust heat recovery devices recover the waste heat of the exhaust gas discharged from the engine by heat exchange with the coolant to improve heating performance. Further, during initial start-up, the temperature of the engine is rapidly increased with the coolant heat-exchanged with the exhaust gas to suitably reduce the friction of the engine, thus improving fuel efficiency.
In addition to the above-described exhaust heat recovery devices, some of the fields in which the research and development for recovery of waste energy is carried out include the construction of a secondary steam engine or a thermoelectric element using the exhaust heat, for example, as follows:
(1) Systems comprising a compounded steam engine including a condenser and an expander and using the energy derived from the steam engine;
(2) Steam turbines as a secondary steam engine using exhaust heat including a condenser, an expander, and first and second superheaters and technology for converting the power generated by the steam turbine into energy for driving the vehicle; and
(3) Systems in which a thermoelectric element using the Peltier-Seebec effect which generates electricity from a temperature difference between the exhaust heat and the environment is mounted in an exhaust system to utilize the electricity generated therefrom.
However, the technology which uses the exhaust heat in the secondary steam engine and the thermoelectric element have a considerably increased weight and a change in structure, and the technology which uses the thermoelectric element has a low energy density and a high back pressure. Therefore, these considerations should be addressed in order to apply these technologies to actual vehicles.
Further, in order to improve the fuel efficiency by reducing the friction of the drive system of the vehicle, e.g., the engine, it is necessary to rapidly increase the temperature of the engine by suitably increasing the temperature of a medium such as coolant, and further it is necessary to rapidly increase the temperature of engine oil or gear box oil.
The conventional device for recovering the exhaust heat by heat exchange between the coolant and the exhaust gas suitably increases the temperature of the coolant using the exhaust heat to increase the temperature of the engine, thereby reducing the friction and improving the fuel efficiency.
However, in order to suitably reduce the friction and improve the fuel efficiency at low temperature, it preferable to increase the temperature of the engine oil or gear box oil rather than to increase the temperature of the coolant.
This can be seen from test results for comparing the reduction in friction loss when the temperature of coolant and oil is increased. Referring to FIG. 2, for example, the reduction in friction loss is considerably increased when the oil temperature is increased rather than when the coolant temperature is increased, from which it can be seen that the heat exchange between the oil and the exhaust gas is more effective than the heat exchange between the coolant and the exhaust gas.
Accordingly, there remains a need in the art for an exhaust heat recovery device that is capable of performing heat exchange between exhaust gas, coolant, and oil by modifying the conventional exhaust heat recovery device which performs heat exchange between the exhaust gas and the coolant.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.